A lab-scale EUV high-intensity exposure setup for small-spot exposures and angular-resolved photoelectron spectroscopy

Abstract

This work investigates extreme ultraviolet (EUV)-induced photoemission in materials relevant for EUV lithography, combining synchrotron-based X-ray photoelectron spectroscopy (XPS and ARPES) measurements with Monte Carlo photoemission modeling. Gold (Au) is used as a reference material to benchmark the model, while ruthenium (Ru) thin films represent a technologically important, but less well-characterized capping material for EUV mirrors and masks. For Au, a comparison between experiment and simulation indicates a good understanding of the underlying physics: core-level peak positions and the shape of the secondary electron region are well reproduced. Remaining discrepancies in the intensity ratio between core levels and secondary electron background are resolved by explicitly including valence-band emission. For Ru, XPS and ARPES demonstrate that in-situ argon (Ar) sputtering effectively removes carbon contaminations and reveals Ru-specific spectral features. While the simulation reproduces Ru core-level energies, it fails to capture it’s complex secondary electron shape, indicating that the underlying non-material-specific inelastic scattering data are inaccurate for Ru. These results establish Au as a benchmark for the model and identify material specific inelastic scattering data as the key limitation for the Ru modelling. A dedicated EUV laboratory system with integrated ARPES is planned to measure such material specific loss functions under realistic EUV hydrogen plasma conditions and to extend these studies to EUV optics, multilayers, and mask materials.